HAT-P-66 b
HAT-P-66 b is a hot Jupiter orbiting the G0 star HAT-P-66 in the constellation Ursa Major. It lies about 3,051 light-years from Earth and was discovered in 2016 using the transit method.
How Big Is HAT-P-66 b?
HAT-P-66 b has a radius of 17.82 times that of Earth, or 1.59 times the radius of Jupiter. Its mass is 249 times that of Earth, giving it a density of 0.24 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is HAT-P-66 b in the Habitable Zone?
HAT-P-66 b orbits inside the inner edge of the habitable zone of HAT-P-66. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HAT-P-66: 1.503–3.521 AU (conservative: 1.903–3.338 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on HAT-P-66 b
The equilibrium temperature of HAT-P-66 b is about 1,896 K (1,623 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on HAT-P-66 b — one full orbit around HAT-P-66 — lasts 2.97 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.044 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.09).
How Was HAT-P-66 b Discovered?
HAT-P-66 b was discovered in 2016 using the transit method, with observations from HATNet.
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is HAT-P-66 b?
HAT-P-66 b is 3,051.0 light-years (935.5 parsecs) from Earth. Light arriving here tonight left the planet about 3,051 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 53,697,600 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. HAT-P-66 b scores 0.05, ranking #5,260 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HAT-P-66
HAT-P-66
- Spectral type
- G0
- Surface temperature
- 6,002 K (Sun: 5,772 K)
- Mass
- 1.25 M☉
- Radius
- 1.88 R☉
- Luminosity
- 4.1200 L☉
- Age
- 4.7 billion years (Sun: 4.6)
Planetary System
HAT-P-66 b is the only planet known to orbit HAT-P-66 so far.
HAT-P-66 b — Complete Data
| Radius | 17.822 Earth radii (1.590 Jupiter radii) |
|---|---|
| Mass | 248.86 Earth masses (0.783 Jupiter masses) |
| Density | 0.24 g/cm³ (Earth: 5.51) |
| Orbital period | 2.97 days |
| Orbital distance | 0.044 AU |
| Eccentricity | 0.090 |
| Equilibrium temperature | 1,896 K (1,623 °C) |
| Earth Similarity Index | 0.05 |
| Distance from Earth | 3,051.0 light-years (935.5 parsecs) |
| Constellation | Ursa Major |
| Discovery method | Transit |
| Discovery facility | HATNet |
| Discovery year | 2016 |
Data: NASA Exoplanet Archive, last updated 2016-09-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HAT-P-66 b
Is HAT-P-66 b habitable?
No — HAT-P-66 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HAT-P-66 b?
HAT-P-66 b is about 3,051 light-years from Earth in the constellation Ursa Major. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 53,697,600 years to get there.
How big is HAT-P-66 b compared to Earth?
HAT-P-66 b has 17.82 times the radius of Earth and about 249 times its mass.
How long is a year on HAT-P-66 b?
One orbit around HAT-P-66 takes 3.0 Earth days — short enough that 123 of its years would fit into one Earth year.
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